Initial reports said he was killed by police, but Las Vegas Metropolitan Police Sheriff Joe Lombardo later said he shot himself.

He is believed to have checked in to the Mandalay Bay Resort and Casino on Thursday and fired out of the window at the crowded streets.

Lombardo said officers found more than 10 guns in the 32nd floor room where Paddock opened fire on concertgoers in the streets below that he worked alone.

He later added that several pounds of ammonium nitrate, a material used to make explosives, was found in Paddock’s car and that investigators found 18 firearms, explosives and several thousand rounds of ammunition in his Mesquite home.

Islamic State has claimed responsibility for the mass shooting, insisting Paddock converted to Islam a few months ago. It has made exaggerated or false claims in the past.

“The Las Vegas attack was carried out by a soldier of the Islamic State and he carried it out in response to calls to target states of the coalition,” the group’s news agency Amaq said, referring to the US-led coalition fighting the group in the Middle East.

Police insisted he worked alone and two senior officials said there was no evidence Paddock had links to international militant groups.

“As this event unfolds we have determined to this point no connection with an international terrorist group,” said Aaron Rouse, the special agent in charge of the Las Vegas office of the FBI.

“We have no idea what his belief system was. Right now, we believe he was the sole aggressor and the scene is static,” he said.

Paddock worked as an accountant, and public records show that he has both a pilot’s and hunting licence.

Authorities say they’re no longer looking for the woman who police believed was an “associate” to Paddock.

Police initially said that the 62-year-old woman was his roommate in Mesquite, Nevada.

Police now say they’ve located her and determined she wasn’t involved in the mass shooting, as she has been out of the country.

No Chinese nationals were reported among the casualties.

“We did not receive any reports saying Chinese people were injured or killed in the incident,” said a staff member from the Chinese Consulate in San Francisco, which manages affairs in Las Vegas.

A three-day Route 91 Harvest country music festival performance was underway across Las Vegas Boulevard from the Mandalay Bay hotel when the shooting erupted. Concertgoers reported a burst of weapons fire during Jason Aldean’s performance.

Jake Owen, a country music star who played the set before Jason Aldean’s, wrote on Twitter that “gun shots were ringing off of the stage rigging and road cases”.

He suggested that the gunman was aiming at the stage at times. “No one knew where to go,” he said.

Video posted on social media showed the open-air concert underway when bursts of automatic gunfire rang out in rapid succession. Dozens of concertgoers dropped to the ground, screaming, while others ran.

The shooting went on for about more than 30 seconds before the music stopped, and another burst was heard later.

“Get down, stay down,” one woman shouted. Another wave of gunshots followed soon after.

“I thought it was like bottle rockets going off,” said Seth Bayles, of West Hollywood, California. “Then we saw people dropping. We saw someone get hit and then we started running.”

Bayles said Aldean was quickly pulled offstage, and soon after, the band was taken off.

Two men near the casino said they heard a helicopter with a loudhailer yelling “Go! Go! Go!” as the incident unfolded. Others said they saw police and SWAT teams streaming into the Mandalay Bay casino.

Alarm spread up and down the strip as news of the shootings spread.

Kevin Daly, 58, of Long Beach, California, said he had been playing pai gow at the MGM Grand hotel, along the road from the concert venue and was near the entrance when chaos erupted.

“All these people started running and screaming, and then that stopped for about a minute, and then more people started coming in the other way and ran through where I was,” he said.

“There were so many people walking and running and people crying and people saying there’s an active gunman on the street, so I finally asked one of the waitresses what’s going on and she said the gunman is outside of the casino.”

Daly said the entire area was put on lockdown so he went upstairs to his room. “Out the windows, we can see Mandalay Bay, we can see all the police cars and all the lights and there are helicopters all over the place.”

Officials at McCarran International Airport reported that some flights have been diverted in the wake of the shootings. “Expect delays,” the airport said on Twitter.

Parts of I-15 near the Strip were also shut down, and hotel guests across the Strip were ordered to shelter in place.

Aldean was the final act of the festival, while dozens of others had played over the course of the weekend, including Church, Hunt and Maren Morris. In numerous tweets, artists communicated with fans and followers, expressing their sorrow and prayers for anyone injured and telling loved ones that they were safe.

Jake Owen, who played the main stage before Aldean, tweeted: “Praying for everyone here in Vegas. I witnessed the most unimaginable event tonight. We are okay. Others aren’t. Please pray.”

Additional reporting by Associated Press, Agence France-Presse, Reuters, The Guardian, Tribune News Service